Hello everyone,
I studied Psychology and I will join an Occupational (Work) Psychology Master program on September.
I am accepted at Leeds, Nottingham, Loughborough and Sheffield.
Nottingham program is from the Medicine department and the other are held in
the Business Schools of each Uni.

I am trying to establish which Uni presents better Career prospects but I am not sure what rankings to check.
Should I only consider the Business schools and Medicine for Nottingham , Psychology ranking or maybe Overall ?

None of them, they are all manipulated nonsense. Look for the best style of teaching that suits you, the academics you'd like to work with, the facilities you personally will use, the costs and available funds, and where you would like to live. Your personal success on the course is far more important to your future employability than any marketing tool of a league table designed to sell newspapers or data products.

As above. Even if you could work out a way to quantify 'career prospects' (difficult) and directly compare courses (very difficult) would you just pick the course with the highest value? There are many factors in choosing a postgrad course. FWIW 'career prospects' wasn't a factor when I chose my postgrad degrees.